One thing I have learnt in life is that everyone is replaceable, even if it doesn't appear so at the time. He has been with us two years and he will be taking a lot of intellectual capital to spurs, however we will have sucked him dry of his knowledge as well. What's more is that you don't get better by doing the same thing year in year out. A new person in that role will bring new ideas which can then be blended into the existing process and improve it.
one thing our club seems to have cracked is an overreliance on any one man. Therefore farewell and good luck, because you are going to need it at spurs.